The need to interrupt the high speed fluid jets widely used to cut food, paper and other products has been known for years. The fluids used to cut food products are generated with very high pressures, and do not use abrasives such as are used when cutting metals or stones. The high pressure allows the fluid to cut through the food products very quickly and in any direction. This ability has led to the development of cutter control and motion systems that also move very rapidly and in any direction.
In moving rapidly to cut the food products, it is advantageous at times to block the fluid to allow the path of the stream to cross over the food without cutting it. The jet stream may be blocked during a cutting procedure of an individual portion, or when an individual cutter crosses over a stream of products to reach a destination on the far side of the stream. Typically, the blocking of the jet stream has been achieved by inserting a metal pin into the stream, either with a pneumatic cylinder, or by pivoting the pin into the stream with an electric motor.
When modern food portioning machines draw intricate patterns at high speeds, the full block and unblock cycle needs to be completed in a matter of milliseconds. Crossing between the blocked and unblocked position must happen within a few milliseconds to draw sharp shapes and corners. Additionally, while a delay between sending the actuating signal and initial movement can be acceptable within the limits noted above, it must be very consistent—within a range of a few milliseconds.
Industrial food processes can only be viable if they are extremely efficient, with high production rates, and long runtimes with very low levels of scheduled and unscheduled downtime. The environment that jet blockers operate in is extremely hostile. The atmosphere is almost continuously wet and hot, and replete with organic debris from the food product being cut. The movement of the jet blocker causes high frequency shaking and vibrations with movements with accelerations up to 8 gs. Also, the pressure from the waterjets causes continuous erosion of machine parts, adding to downtime and high maintenance costs. Daily cleaning cycles include high-pressure washing and harsh chemicals that can be at either extreme of the pH scale. The desired life cycle for the blocker is in the area of 150 million cycles in this environment, with under a total of 1% scheduled and unscheduled downtime for the machine during the routine 16-hour-per-day operations.
The high-pressure waterjets can generate sound levels over 100 db, requiring that personnel working near the machine wear hearing protection. Sound levels are often reduced when cutting stones or metal by performing the cut under water; however, that option is not possible with food products. Other approaches to reducing the sound levels include disrupting the jet after it has cut through the product. It has been noted that the greater the length of the jet stream, the higher the sound levels, and so the closer to the nozzle the jet stream is disrupted, the greater the reduction in sound levels. Blocking the jet for cutting operations with jet blockers will also achieve sound reductions in the times they are blocking the jet stream.
Various methods and apparatus have been used to controllably interrupt a high-speed water jet. One such method of interruption is to use a linear actuator to insert an object between the high-speed water jet and the product to be cut. Typically, a pneumatic linear actuator forces a blocker pin into the path of the water jet to interrupt the flow of the cutting stream and a spring provides a retracting force for the plunger pin. Existing pneumatic blocker pin devices are capable of reaching closure times of 50-90 milliseconds and thereby limiting the speed at which products may be cut by the water jet.
The fluid jets the blockers must block are jet streams that can be as high as 87,000 psig in pressure. The high-pressure blocker mechanisms wear rapidly, not only with direct impingement from the fluid jet, but also from indirect sprays from higher pressure blocked water. Blocker pins therefore require frequent manual re-positioning of their surfaces to allow a new wear surface to be presented to the fluid jet. Pins may undergo several manual adjustments, and then must be replaced entirely—a process that may cause unwanted and expensive downtime, and if done improperly, reduce the service life of the device.
In another type of apparatus, actuators have been used that insert a blocking pin into the jet stream with rotating electric motors that move a pin into the stream with a rotating motion. These actuators may be sufficiently fast to meet the speed requirements, but have other shortcomings that limit their life, and contribute to unacceptable levels of downtime for routine maintenance.
The blocking pin is prone to relatively rapid wear. An adjustment mechanism allows moving the pin further in, or out, to present a new point on the pin to block the water. After 5 to 10 adjustments, the pin is removed from the blocker and turned end-for-end to allow another 5 to 10 adjustments. This requires a partial disassembly of the blocker mechanism. After both ends of the pin are worn through, the pin needs to be replaced entirely. When rotating or replacing the pin, the seals, gaskets and screws, etc., are often damaged, allowing water to enter the actuating mechanism, causing premature failure of the entire device.
In existing designs of jet blockers, the material that interrupts the fluid stream is much harder than the food being cut, but still will be eroded to the point of failure, and the time of failure is unpredictable. This unpredictable failure of the blocking function, as well as other parts prone to failure, can be a cause of expensive downtime to producers using the systems. Most pins are made of relatively expensive materials such as Stellite and carbide compounds, selected to last as long as possible, due to their resistance to wear. Long wear allows the longest time possible between the unpredictable failure events and manual replacement of the pins requiring mechanical replacement of the pins and subsequent downtime.
What is lacking in the art is a water jet blocker and method of use that will provide rapid movement, and precise control of the blocker while allowing predictable erosion, and easy replacement of the blocking material to prevent unscheduled downtime. The present invention seeks to address this need, and seeks to provide further related advantages.